Strandings of marine animals in Southern California have increased dramatically in the past few weeks. The mortality rate is up and rescue teams and care centers are overrun with a large number of ailing sea lions and birds. We asked David Caron, a professor in USC’s department of Biological Studies, if he could explain what is causing these animals’ illness and death. He responded with the following:

Domoic acid is a powerful neurotoxin produced by a specific group of microscopic algae that sometimes blooms in coastal waters. If the algae are abundant and producing toxin, they can be strained from the water by plankton-eating fish such as sardine and anchovy. The toxin contained in the algae is concentrated in the stomachs of these fish during a toxic algal bloom. Marine mammals or sea birds eating fish laden with toxin can ingest sufficient domoic acid in the stomachs of their prey to experience symptoms of domoic acid poisoning. These symptoms can include a variety of neurological disorders including disorientation and seizures, and in severe cases death.

There has been an increased number of animals (sea lions, dolphins and some birds) stranding on local beaches during the past few weeks. Many of these animals exhibited symptoms of domoic acid poisoning. We have confirmed the presence of domoic acid in fluids collected from a number of these animals, indicating that a toxic bloom is taking place in coastal waters, although the specific location and extent of the bloom is not known.